Preparation of metal bromides from a basic metal compound and bromine in the presence of a reducing agent has been known for a long time.
U.S. Pat. No. 1,775,598 discloses the use of reducing agents which are converted into water and/or gases. These may be nitrogen-containing organic or inorganic compounds such as urea, cyanamide, ammonia, ammonium carbonate, ammonium bicarbonate, formamide, carbamates, and ammonium cyanide; or easily decomposable organic acids such as formic or oxalic acid; or ammonium or metal derivatives of these compounds (e.g. calcium nitride, metal formates, or oxalates. Substances which give similar reducing agents on mixing (e.g. hexamethylenetetramine) are also disclosed. British Pat. No. 285,915 has a similar disclosure.
U.S. Pat. No. 1,843,355 discloses use of charcoal as a reductant. U.S. Pat. No. 1,863,375 and 2,007,758 both relate to use of ammonia as the reducing agent. U.S. Pat. No. 1,916,457 pertains to use of carbon as a reductant, principally in the formation of sodium bromate.
U.S. Pat. No. 2,269,773 also discloses use of a variety of reducing agents and alternative reaction sequences. U.S. Pat. No. 4,083,942 discloses use of formic acid as a reactant, and illustrates the process with the following equation: EQU Ca(OH).sub.2 +HCOOH+Br.sub.2 .fwdarw.CaBr.sub.2 +CO.sub.2 +H.sub.2 O
In the process of that patent, bromine and the alkaline compound are alternatively and incrementally added to an aqueous mixture of formic acid and a less than equivalent amount of metal compound, while maintaining the pH below 7.0.
U.S. Pat. No. 3,462,241 relates to the reaction of lime and bromine in the absence of a reductant: EQU 2Br.sub.2 +2Ca(OH).sub.2 .fwdarw.Ca(OBr).sub.2 +2H.sub.2 O+CaBr.sub.2
The yield of calcium bromide by this method is about 9-12%.
No reference was found relating to the use of formaldehyde as disclosed by the process of this invention.